1. Field of the Invention
The invention relates to a cooling apparatus for a water-cooled engine, and a method of controlling a cooling apparatus for a water-cooled engine. More particularly, the invention relates to improvement in a control structure of a cooling apparatus, for improving restartability of an engine when the engine is restarted immediately after the engine has been operated under a high load.
2. Description of the Related Art
A water-cooled engine is cooled by circulating coolant in a water jacket formed in a cylinder head and a cylinder block, and delivering air to a radiator to cool the coolant whose temperature has been increased by heat received from the engine. In many water-cooled engines, for example, in the water-cooled engine provided in a vehicle, a coolant temperature is detected, and when the coolant temperature is equal to or higher than a set value, a radiator fan is operated to deliver air to the radiator, so that efficiency of cooling the engine is increased.
When the engine is stopped immediately after a vehicle has traveled on an upward slope or at a high speed and therefore the engine has been operated under a high load for a long period, a temperature around the engine may sharply increase due to the stop of the radiator fan. In this situation, the temperature of fuel may increase, and accordingly, vapor may be generated in a delivery pipe. Thus, when the engine is restarted in a high-temperature condition, the vapor in the delivery pipe may be sucked into an injector. As a result, fuel may not be appropriately injected, and the startability of the engine and idling stability after the engine start may deteriorate. Therefore, when the engine is restarted in a high temperature condition, it is necessary to quickly decrease the temperatures of oil and coolant for the engine, in order to ensure the startability and idling stability.
Thus, Japanese Patent Application Publication No. 08-200067 (JP-A-08-200067) describes a technology in which if a coolant temperature and an intake air temperature in an engine are high at the time of engine start, and it is determined that the engine is restarted in a high temperature condition, a set value of the coolant temperature related to the operation of a radiator fan is made lower than a normal threshold value, so that the operation of the engine is stabilized after the restart of the engine in a high temperature condition.
In the above-described technology, it is possible to quickly decrease the temperatures of oil and coolant for the engine after the start of the engine. Therefore, it is possible to increase the stability of the operation of the engine after the restart of the engine in a high temperature condition. However, when the radiator fan is operated after the start of the engine, it takes a certain time to decrease the temperatures of oil and coolant for the engine, and therefore, the effect of improving the startability of the engine at the time of restart in a high temperature condition is limited.